java图形界面的一个小疑点，纠结了好久了

import java.awt.*;import java.awt.event.*;import javax.swing.JFrame;class Selection extends JFrame implements ActionListener {    Button c1;    Panel p = new Panel();    Panel p1 = new Panel();    public Selection(String s) {        super(s);        Label r = new Label("请选择你要的服务");        c1 = new Button("查询余额");        p.add(r);        p1.add(c1);        this.setLayout(new GridLayout(6, 1));        this.add(p);        this.add(p1);         // /*各种服务功能*/        this.addWindowListener(new WindowAdapter() {            public void windowClosing(WindowEvent e) {                System.exit(0);            }        }); // closing the window        c1.addActionListener(this);        setBounds(150, 150, 200, 200);        setVisible(true);    }// 构造函数    public void actionPerformed(ActionEvent e){           if(e.getSource()==c1){           dispose();           BalanceChecck bc=new BalanceChecck("查询余额");}}    }/*查询余额*/class BalanceChecck extends Frame implements ActionListener {    Button ba;    Panel a=new Panel();    public BalanceChecck(String s){    super(s);    Button ba=new Button("返回");    this.add(a);    a.add(ba);    ba.addActionListener(this);    setLayout(new FlowLayout());    setVisible(true);    setBounds(150, 150, 200, 200);        this.addWindowListener(new WindowAdapter() {        public void windowClosing(WindowEvent e) {            System.exit(0);        }    }); // closing the window           }//public        public void actionPerformed(ActionEvent e){        if(e.getSource()==ba){            Selection s = new Selection("选择");            dispose();            }//if    }}public  class test {    public static void main(String args[]) {        new Selection("ff");            }}

 Button ba;    Panel a=new Panel();    public BalanceChecck(String s){    super(s);    Button ba=new Button("返回");    this.add(a);